CHE141
Chapter 2
Chapter 2
Atoms, Molecules, and Ions
1. Methane and ethane are both made up of carbon and hydrogen. In methane, there are
12.0 g of carbon for every 4.00 g of hydrogen, a ration of 3:1 by mass. In ethane,
there are 24.0 g of carbon for every 6.00 g of hydrogen, a ratio of 4:1 by mass. This
is a statement of the law of _________________.
(a). constant composition
(b).multiple proportions
(c). conservation of matter
(d). conservation of mass
(e). octaves
Explanation: The Law of Multiple Proportions states that “if 2 elements A and B
combine to form more than one compound, the masses of B that can combine with a
given mass of A are in the ratio of small whole numbers”.
2. Which statement below correctly describes the responses of alpha, beta, and gamma
radiation to an electric field?
(a). Both beta and gamma are deflected in the same direction, which alpha shows
no response.
(b). Both alpha and gamma are deflected in the same direction, while beta shows
no response.
(c). Both alpha and beta are deflected in the same direction, while gamma shows no
response.
(d). Alpha and beta are deflected in opposite directions, while gamma shows no
response.
(e). Only alpha is deflected, while beta and gamma show no response.
Explanation: Alpha particles are positively charged and beta particles have negative
charges. As a result of their opposite charges they are deflected in opposite
directions.
3. ______________ and _____________ reside in the atomic nucleus.
(a). Protons, electrons
(b). Electrons, neutrons
(c). Protons, neutrons
(d). None of the above
Explanation: Only protons and neutrons are in the nucleus, electrons are always
outside the nucleus.
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CHE141
Chapter 2
4. 200 pm is the same as ____________Å.
(a). 2000
(b). 20
(c). 200
(d).2.00
Explanation: One pm = 1 x 10-12 m and 1 angstrom = 1x 10-10 m. Thus 100 pm = 1
angstrom and hence 200 pm = 2.00 Å
5. The atomic number indicates ___________.
(a). the number of neutrons in a nucleus
(b). the total number of neutrons and protons in a nucleus
(c). the number protons or electrons in a neutral atom
(d). the number of atoms in 1 g of an element
Explanation: The atomic number not only indicates the number of protons but also
the number of electrons in a neutral atom since the number of protons in a neutral
atom = number of electrons.
6. Which pair of atoms constitutes a pair of isotopes of the same element?
!
!
!
!
(a). 146 X
(b). 146 X
(c). 179 X
(d). 19
10 X
14
7
12
6
17
8
19
9
X
X
X
X
Explanation: Isotopes of an element are atoms of the same element with same
number of protons but different number of neutrons. Only choice (b) has 2 atoms of
X with 6 protons and 8 and 6 neutrons respectively.
7. Elements in Group 8A are known as the ___________.
(a). chalcogens
(b). alkali metals
(c). noble gases
(d). alkaline earth metals
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CHE141
Chapter 2
8. _____________ are found uncombined, as monatomic species in nature.
(a). Halogens
(b). Alkali metals
(c). Noble gases
(d). None of the above
Explanation: Since these elements do not react with other elements they are known
as noble gases.
9. When a metal and a nonmetal react, the _______ tends to lose electrons and the
_____________ tends to gain electrons.
(a). metal, metal
(b).metal, nonmetal
(c). nonmetal, metal
(d). None of the above, these elements share electrons.
Explanation: The reaction between a metal and nonmetal is possible due to the loss
of electrons by the metal (forming cations) and gain of electrons by the nonmetal
(forming anions.
10. The empirical formula of a compound with molecules containing 12 carbon atoms, 14
hydrogen atoms, and 6 oxygen atoms is ___________.
(a). C12H14O6
(b). C2H4O
(c). CH2O
(d).C6H7O3
Explanation: The empirical formula is always the simplest possible whole number
ratio between the atoms of the molecules.
11. ____________ typically form ions with a 2+ charge.
(a). Transition metals
(b). Halogens
(c). Alkaline earth metals
(d). Alkali metals
Explanation: The alkaline earth metals are in group 2A of the periodic table and lose
2 electrons to form cations with 2 positive charges.
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CHE141
Chapter 2
12. Magnesium reacts with a certain element to form a compound with the general
formula MgX. What would the most likely formula be for the compound formed
between potassium and element X?
(a). KX
(b). K2X2
(c). K2X3
(d). KX3
(e). None of the above
Explanation: In the compound MgX, X must have 2 negative charges since Mg will
always have 2 positive charges. The element K will always form an ion with 1
positive charge and hence the only combination of K and X could be K2X, which is
not one of the options
13. The charge on the manganese in the salt MnF3 is ______________.
(a). +1
(b). -1
(c). +3
(d). -2
Explanation: Since every F has one negative charge, the Mn can have only 3 positive
charges.
14. Barium forms an ion with a charge of _________.
(a). +1
(b). -2
(c) +3
(d).None of the above
Explanation: Barium is in group 2A of the periodic table and forms ions with only 2
positive charges.
15. Aluminum forms an ion with a charge of___________.
(a). +2
(b). -3
(c). +3
(d). +1
16. Iodine forms an ion with a charge of _____________.
(a). -7
(b). +1
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CHE141
Chapter 2
(c). -1
(d). +2
17. Oxygen forms an ion with a charge of __________.
(a). -1
(b). +2
(c). -3
(d).-2
18. Predict the empirical formula of the ionic compound that forms from sodium and
fluorine.
(a). Na3F
(b). Na2F
(c). NaF2
(d).None of the above
19. Predict the empirical formula of the ionic compound that forms from magnesium and
oxygen.
(a). Mg2O
(b).MgO
(c). MgO2
(d). Mg3O2
20. The correct name for H2CO3 is _______.
(a). carbonous acid
(b). dihydrogencarbonate
(c). carbohydrate
(d).carbonic acid
21. The correct name for H2SO3 is _______.
(a). sulfuric acid
(b). dihydrogensulfite acid
(c). hydrosulfuric acid
(d).sulfurous acid
22. The correct name for HC1O3 is _______.
(a). hydrochloric acid
(b). perchloric acid
(c). chloric acid
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CHE141
Chapter 2
(d). None of the above
23. The correct name for HBrO2 is _________.
(a). bromic acid
(b). hypobromous acid
(c). hypobromic acid
(d).bromous acid
Explanation: For both questions 22 and 23 you must know these names, there is no
other trick.
24. The correct name of the compound Na3N is __________.
(a). sodium nitride
(b). sodium azide
(c). trisodium nitride
(d) sodium (III) nitride
Explanation: Since Na is in group IA, there is no need to indicate the number of
sodium ions in this compound.
25. The correct formula for molybdenum(IV) hypochlorite is __________.
(a). Mo(C1O3)4
(b). Mo(C1O2)4
(c). Mo(C1O)4
(d). Mo(C1O4)4
26. The ions Ca2+ and PO43- form a salt with the formula ___________.
(a). CaPO4
(b). Ca2(PO4)3
(c). Ca2PO4
(d).Ca3(PO4)2
Explanation: The least common multiple of 2 and 3 is 6. To be able to reach this
number you need 3 Ca2+ ions and only 2 phosphate ions.
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CHE141
Chapter 2
27. Which one of the following is not one of the postulates of Dalton’s atomic theory?
(a). Atoms are composed of protons, neutrons, and electrons.
(b). All atoms of a given element are identical; the atoms of different elements are
different and have different properties.
(c). Atoms of an element are not changed into different types of atoms by chemical
reactions: atoms are neither created nor destroyed in chemical reactions.
(d).Compounds are formed when atoms of more than one element combine; a given
compound always has the same relative number and kind of atoms.
Explanation: Dalton did not know about the existence of subatomic particles.
28. Consider the following selected postulates of Dalton’s atomic theory:
(i) Each element is composed of extremely small particles called atoms.
(ii) Atoms are indivisible.
(iii) Atoms of a given element are identical
(iv) Atoms of different elements are different and have different properties.
Which of the postulates is (are) no longer valid?
(a). (i) and (ii)
(b). (ii) only
(c). (iii) only
(d).(ii) and (iii) only
Explanation: Atoms are divided into subatomic regions such as the nucleus and
orbitals and while the existence of isotopes proves that not all atoms of an element are
identical
29. Of the following, the smallest and lightest subatomic particle is the __________.
(a). neutron
(b). proton
(c). electron
(d). alpha particle
30. All atoms of a given element have the same __________.
(a). mass
(b). number of electrons and neutrons
(c). number of neutrons
(d).number of protons
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CHE141
Chapter 2
31. Which combination of protons, neutrons, and electrons is correct for the isotope of
63
Cu?
copper, 29
(a). 29p+,34nº, 29e(b). 29p+,29nº,63e(c). 63p+,29nº,63e(d). 34p+,29nº,34e32. Which isotope has 45 neutrons?
(a).
80
36 Kr
78
34 Se
(b).
(c). 80
35 Br
34
(d). 17 Cl
!
! 33. Isotopes are atoms of the same element that have the same number of __________
but differing number of ___________.
(a). protons, electrons
(b). neutrons, protons
(c). protons, neutrons
(d). electrons, protons
34. Different isotopes of a particular element contain the same number of _________.
(a). electrons
(b). neutrons
(c). protons and neutrons
(d). protons, neutrons, and electrons
35. In the periodic table, the elements are arranged in _________.
(a). alphabetical order
(b).order of increasing atomic number
(c). order of increasing metallic properties
(d). order of increasing neutron content
36. Elements __________ exhibit similar physical and chemical properties.
(a). with similar chemical symbols
(b). with similar atomic masses
(c). in the same period of the periodic table
(d).in the same group of the periodic table
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CHE141
Chapter 2
37. An element in the upper right corner of the periodic table _________.
(a). is either a metal or metalloid
(b). is definitely a metal
(c). is definitely a non-metal
(d). is either a metalloid or a non-metal
38. An element that appears in the lower left corner of a periodic table is _________.
(a). either a metal or metalloid
(b).definitely a metal
(c). either a metalloid or a non-metal
(d). definitely a non-metal
39. Which one of the following does not occur as diatomic molecules in elemental form?
(a). oxygen
(b). nitrogen
(c). sulfur
(d). hydrogen
40. A molecular formula always indicates __________.
(a). how many of each atom are in a molecule
(b). the simplest whole-number ratio of different atoms in a compound
(c). which atoms are attached to which in a molecule
(d). the isotope of each element in a compound
41. An empirical formula always indicates___________.
(a). which atoms are attached to which in a molecule
(b). how many of each atom are in a molecule
(c). the simplest whole-number ratio of different atoms in a compound
(d). the geometry of a molecule
42. The molecular formula of a compound is always ____________ the empirical
formula.
(a). more complex than
(b). different from
(c). a whole number multiple of
(d). the same as
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CHE141
Chapter 2
43. There are ________ protons, ________ neutrons, and ________ electrons in 131I-.
(a). 131, 53, and 54
(b). 131, 53 and 52
(c). 53, 78, and 54
(d). 53, 131, and 52
(e). 78, 53, and 72
44. Which species has 48 electrons?
+2
(a). 118
50 Sn
+4
(b). 116
50 Sn
+2
(c). 112
48 Cd
(d). 68
31 Ga
45. Which pair of elements is most apt to form an ionic compound with each other?
(a). calcium, sodium
(b).barium, bromine
(c). oxygen, fluorine
(d). sulfur, fluorine
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